Static Dissipating additives are used in many distillate fuels, including diesel, aviation turbine (jet) fuels, and gasoline, to reduce the risk of static charges being built up in a fuel as it flows through pipes and high surface area filters. The built up of static charges can approach 100 kV and even with proper bonding and grounding it is possible for static discharges to occur resulting in fires and explosions. In general the energy of a discharge must be over 1 kV (or under −1 kV) for a localized discharge or 30 kV (or under −30 kV) for a brush discharge to be incendiary to distillate fuels. In aviation fuels there is currently only a single approved static dissipating additive for maintaining low surface voltages and for increasing voltage relaxation rates of a fuel. A combination of conductivity additive is not only discouraged by regulation in aviation fuels but requires extensive testing to show that any new or additional additive to an aviation fuel does not counteract or adversely affect any other additive in the fuel. Accordingly, the only approved conductivity additive for aviation fuel is an additive that is a combination of polysulfone/amine epichlorohydrin polymer in combination with sulfonic acid, a quaternary ammonium, and an aromatic solvent.
It is known that trace materials in hydrocarbon fuels such as acids, alcohols, amines, and mercaptans enables the fuel to be much more easily ionized to give electrically charged fragments than the pure, unadditized fuel. Unfortunately, many of the foregoing compounds and other impurities are always present in fuels, thus the overall tendency of the fuel to generate charge is not predictable and varies at least 100-fold. The magnitude of charge generated also depends on flow velocity. Thus fine filters, such as filter-coalescers can give enormous electrostatic charging because of the huge surface area compared to pipes and fittings. Static charges can also build up rapidly on the surface of fuel in tanks. Because of the unknown level of impurities in a fuel, there is a need to maintain a low fuel surface voltage without adversely affecting the conductivity or surface voltage relaxation time of the fuel.
In view of the foregoing, embodiments of the disclosure provide additive composition mixtures and methods for synergistically maintaining low surface voltages of distillate fuels. In one embodiment there is provided a synergistic conductivity improver additive composition for a distillate fuel. The additive composition includes: A) a mixture of (i) alkenyl polysulfone polymer, (ii) C16-C24 substituted maleic/polyamine copolymer, (iii) sulfonic acid, and (iv) aromatic solvent; and B) a mixture of (i) alkenyl polysulfone polymer, (v) polymeric reaction product of a C8-C18 aliphatic amine or diamine with epichlorohydrin; (iii) sulfonic acid, (iv) aromatic solvent; and optionally (vi) a quaternary ammonium compound. The additive composition contains from 30 to 60 wt. % component (A) and from 30 to 60 wt. % component (B) based on a total weight of the additive composition.
In another embodiment, there is provided a method for synergistically maintaining an absolute value of surface voltage of a distillate fuel below 1000 volts. The method includes providing a distillate fuel and adding to the fuel A) from about 0.25 to about 2.5 mg/L by weight based on a total volume of the fuel composition of a mixture of (i) alkenyl polysulfone polymer, (ii) hydrocarbyl substituted maleic/polyamine copolymer, (iii) sulfonic acid, and (iv) aromatic solvent; and B) from about 0.25 to about 2.5 mg/L by weight based on a total volume of the fuel composition of a mixture of (i) alkenyl polysulfone polymer, (v) polymeric reaction product of a C8-C18 aliphatic amine or diamine with epichlorohydrin; (iii) sulfonic acid, (iv) aromatic solvent; and optionally (vi) a quaternary ammonium compound.
Yet another embodiment provides a method for synergistically maintaining an absolute value of surface voltage of a distillate fuel below 1000 volts. The method includes: providing a first distillate fuel and adding to the first fuel a fuel additive (A) comprising from about 0.25 to about 2.5 mg/L by weight based on a total volume of the first fuel composition of a mixture of (i) alkenyl polysulfone polymer, (ii) hydrocarbyl substituted maleic/polyamine copolymer, (iii) sulfonic acid, and (iv) aromatic solvent; providing a second distillate fuel and adding to the second fuel a fuel additive (B) comprising from about 0.25 to about 2.5 mg/L by weight based on a total volume of the second fuel composition of a mixture of (i) alkenyl polysulfone polymer, (v) polymeric reaction product of a C8-C18 aliphatic amine or diamine with epichlorohydrin; (iii) sulfonic acid, (iv) aromatic solvent; and optionally (vi) a quaternary ammonium compound; and mixing the first fuel and the second fuel in a volume ratio of 0.1:1 to 10:1.
Another embodiment of the disclosure provides a distillate fuel composition that includes a major amount of distillate fuel and minor conductivity improving amount of: A) a mixture of (i) alkenyl polysulfone polymer, (ii) C16-C24 substituted maleic/polyamine copolymer, (iii) sulfonic acid, and (iv) aromatic solvent; and B) a mixture of (i) alkenyl polysulfone polymer, (v) polymeric reaction product of a C8-C18 aliphatic amine or diamine with epichlorohydrin; (iii) sulfonic acid, (iv) aromatic solvent; and optionally (vi) a quaternary ammonium compound.
An advantage of the embodiments of the disclosure is that a fuel, particularly an aviation or jet fuel may be maintained at a synergistically low surface voltage while not adversely affecting the conductivity or voltage relaxation time of the fuel. The synergistically low surface voltage achieved by the presence of two different types of amine polymers from conductivity improving additives was surprising and quite unexpected. In generally, a mixture of polysulfone and amine polymer effectively raises conductivity and increase charge relaxation rates, but may also increase the amount of charge generated when a fuel passes through pipes and filters. The magnitude and direction of the charge (i.e. positive or negative) is determined by pipe material, plastic versus metal, inherent fuel properties, and the additives used. Traditional conductivity additives contain a polysulfone and an epichlorohydrin/diamine polymer. However, a fuel that includes polysulfone and the two different amine polymers described herein provides a lower surface voltage than can be achieved by a conductivity additive or fuel containing only one of the amine polymers. Depending on the formulation of the additive the fuel may have an overall negative or positive net charge.